Recent studies have shown the feasibility of gene therapy for the treatment of AIDS. HIV regulated expression of the gene for Diphtheria toxin A fragment (IV-DTA) confers resistance against HIV infection in human cell lines. One of the major problems of gene therapy is the effective delivery of the therapeutic gene into target cells. This project will explore and establish means to deliver HIV-DTA constructs, available from Project 1, into a variety of cells, using liposomes as carriers and transfection agents. The most effective cationic liposome composition for the delivery of HIV-DAT plasmids to monocytic and lymphocytic cell lines, and peripheral blood mononuclear cells and macrophages will be established. It will be determined whether the HIV- DTA plasmid encapsulated in liposomes with prolonged circulation in the blood steam and with the ability to extravasate into tissues, can be delivered into macrophages. Whether the HIV-DTA plasmids encapsulated in pH-sensitive liposomes can be delivered effectively to monocyte/macrophages will be determined. The protective effect of the delivered HIV-DTA against de novo HIV-1 infection in cell lines and primary cells will be evaluated, and the stability of expression of the genes will be determined. These studies will constitute a foundation for the liposome-mediated delivery of HIV-DTA constructs into cells in the SCID-Hu mouse model in Project 9001.